Project Summary/Abstract Irradiation-induced hyposalivation and irreversible submandibular gland (SMG) and tongue damage are among the most common and harmful side-effects of radiation therapy during treatment for head and neck cancers. Patients with irreversible hyposalivation must live with a plethora of side-effects including: consistent dry mouth, tooth-decay, inflammation, fungal injection, and problems chewing and swallowing. A more complete understanding of the development of the SMGs and tongue is necessary for devising more effective regenerative strategies for these patients. This proposal aims to elucidate the molecular mechanisms involved in early SMG and tongue development. Specifically, I will examine Sonic Hedgehog (Shh)- dependent mechanism of spatially defined transcriptional networks in the mandible to initiate both SMG and tongue development. Shh signaling is transduced via the Gli transcription factors, which can be processed into transcriptional activators (GliA) or repressors (GliR). This proposed work focuses on understanding how Gli interaction with co-factors and the downstream effects of Gli- mediated Shh signaling contribute to development of tissues within the mandibular prominence. Specifically, in Aim 1 I will ask if GliA requires co-factor activity to initiate spatially restricted transcriptional networks in the developing mandibular prominence with the hypothesis that Hand2 functions as a GliA co-factor to induce glossal transcriptional networks. In Aim 2, I will ask if Gli- dependent transcription is necessary for controlling epithelial proliferation and branching morphogenesis of the SMG tubules by testing the hypothesis that GliA directly activates Nrg2 in the SMG to induce epithelial proliferation and initiate branching morphogenesis. We aim to investigate the dynamic roles of Shh signaling by conditionally knocking out GliA activity and perturbing Hand2 expression in mandibular tissues. Altogether, this study is important for advancing our understanding of the complex molecular dynamics of SMG and tongue development. Understanding these complex processes can influence future methods for developing regenerative therapies for head and neck cancer patients who experience irreversible radiation-induced SMG and lingual damage.